The present invention relates to plant cultivating devices. More specifically, the invention relates to devices for growing plants from seeds in a nutrient solution. Such devices, hereinafter will be referred to as "soilless plant growing devices" when applicable.
Various techniques for growing farm products in an aqueous nutrient solution are well known in the art and a variety of soilless plant growing devices have been proposed. For instance, a device for hydroponically growing plants such as cabbage and lettuce has been disclosed in the specification of U.S. Pat. No. 4,037,460.
The conventional device is designed to stably float plants on the surface of water in the manner shown in FIGS. 1A and 1B. The conventional device has a plurality of rafts 21. The rafts 21 are formed of floating members 24 and 25 made of material of high buoyancy such as polystylene with foamed plastic or wood bonded to both surfaces of a breakable porous film 26 in such a manner that a pair of floating members 24 and 25 form one raft 21. Each pair of floating members 24 and 25 has one opening 27 at the center.
The above-described conventional device is used as follows. First, the film 26 is broken through the central openings 27 of the raft after which a seedling is planted in each central opening with the roots and the stem thereof grown respectively below and above the raft. The device is meritorious in that, as the film 26 is made of moisture absorbing material, plants can be grown directly from seeds.
However, the conventional device is disadvantageous in the following points. The device is so designed that only one seedling or seed can be placed on one raft. Therefore, depending on the kinds of plants to be cultivated, the device needs a considerably large cultivation area and it is difficult to grow plants high in density. Thus, the device is not economical. In growing plants from seeds, the seeds are placed on the film in the openings of the raft. Soon after sprouting, the roots break the film. Accordingly, it is impossible to re-use the device for growing plants from the seeds.